Color television picture tube



Nov. 12, 1968 R. D. KARR 3,411,029

COLOR TELEVISION PICTURE TUBE Filed April 4, 1966 2 Sheets-Sheet 1 lflllllllifllllllllll!!!"|llll|!!!l.l|l|ll!!l|llllllllllllllllllllllllllillllul5 8 INVENTOR- w 5 CHARD HARP) a2 W F1 g 8 W AT TOR/\IEYS 2 Sheets$heet 2Filed April 4, 1966 TELEVISION SIGNAL j w W i O 1 mm mm WLWLWLW m mm MmT TO m mm l m m m of m w E g g w WM Ms? 7 W F Q M 9 m m I film 8 g 1 w.m I a m 8 3w m mm L a F I a E 3 u am m R z a 1 MW 4 j j fl W; W a 5 L wINVENTOR. RICHARD D. KARI? BY AT TORN E Y5 United States Patent3,411,029 COLOR TELEVISION PICTURE TUBE Richard D. Karr, 1720 Dean YorkLane, St. Helena, Calif. 94574 Filed Apr. 4, 1966, Ser. No. 540,009 7Claims. (Cl. 315-13) ABSTRACT OF THE DISCLOSURE A three-gun colortelevision picture tube and an electron focusing system therefor isdescribed. The tube includes a display screen having three differentcolor radiating materials disposed on the display surface in separatehorizontal rows in a repeating color sequence with adjacent rows ofmaterial radiating a different color upon electron bombardment. Threeelectron guns, one for each of the color radiating materials arepositioned at different elevations for directing electron beams unto thedis play screen. The electron accelerating system of each electron gunassembly includes a dynamic focusing electrode which is disposed betweentwo segments of the initial accelerating electrode. A varying voltagegenerator is coupled to the dynamic focusing electrode to impress uponit a voltage which varies during the scanning of the electron beam overthe display screen substantially in accordance with the variation indistance between the gun assembly and the screen.

The present invention relates generally to three-gun color televisionpicture tubes. More particularly, it pertains to an improved colortelevision picture tube having a new electroluminescent display systemincluding a unique electroluminescent display screen, a new orientationof the electron guns of a three-gun array, and a new electron focusingsystem.

In general, there are presently in use, two types of electro-luminescentdisplay system; to wit the three-gun shadow-mask system and thechromatron system. Both of these display systems are considered to leavemuch to be desired in the way of color reproduction. For example,standard three-gun shadow-mask systems include three electron guns whichgenerate three modulated electron beams, each gun being modulated byseparate color signals; a three-color phosphor-dot display screen; and ashadow-mask having an orderly arrangement of up to 3x10 aperturesinterposed between the guns and display screen. The shadow-mask hasimposed certain limitations on the electro-luminescent display systems.For example, about 85% of the electrons comprising the electron beamsimpinge upon and are collected by the shadow-mask, leaving only 15% ofthe electrons of the beams to pass through the shadow-mask and excitethe phosphor dots. Hence, such systems are characterized by inefiicientuse of the electron beams and comparatively loW image brightness.Furthermore, the shadow-mask is easily magnetized by surroundingexternal fieldseven fields as weak as the earths magnetic field or thosecreated by home appliances. Since this magnetization distorts thefocusing of the beams, the shadow masks must be degaussed to neutralizesuch magnetization. In addition, the three electron beams must beconverged into a precise cluster before passing through the holes in theshadowmask en route to the phosphor dot target. Because of thecriticality of this convergence, the apertures of the shadow-mask mustbe precisely aligned with the phosphor-dot patterns defining theindividual picture elements. The slightest misalignment results in theshadow-mask partially shrouding or blanking the phosphor-dot patternsdefining the picture elements. Concomitant with this partial shroudingis a distortion in the reproduction of colors Patented Nov. 12, 1968 dueto reduction in the intensity of one or more of the beam reaching thedisplay screen.

In an attempt to eliminate the above limitations and disadvantagescharacteristic of three-color phosphor-dot shadow maskelectro-luminescent display systems, chromatron systems were developed.Standard chromatron systems include a single electron beam generatorwhich is modulated sequentially by the three color signals; a displayscreen. Since all chromatron systems use a single eluding red, green andblue radiating phosphors arranged in a repeating color sequence; andfocusing grid wires extending parallel with the phosphor strips adjacentthe display screen. Since all chromatron systems use a single electronbeam and do not require a shadow-mask, they do not have any beamconvergence or magnetization problems. However, defocusing problemsstill exist due to charge accumulation on the grid wires. Because of theelimination of the shadow-mask though, a considerably greater portion ofthe electron beam reaches the display screen of the chromatron systemsin comparison to the shadow-mask type systems, hence enabling thechromatron systems to produce much brighter images.

However, in spite of the apparent advantages that chromatron systemshave over the three-gun shadow-mask systems, they have not gained wideacceptance. The extremely large power requirement, overall circuitcomplexities, and two deflection systems required of the chromatronsystems have discouraged its wide acceptance.

Considerable improvement is therefore to be gained by the rovision as inthe present invention, of an electroluminescent display system whichovercomes those limitations and disadvantages characteristic of priorart systems. More specifically, by eliminating the necessity of ashadow-mask and beam switching which consumes large quantities of power,a simple and low power electroluminescent display system can be realizedwhich faithfully reproduces exceedingly, bright, high resolution imagesand which does not require the annoying periodic degaussing. Otheradvantages will be realized where the electroluminescent display systemof the present invention is provided wtih a dynamic particle focusingsystem capable of converging the electrons of a beam to a point whichremains coincident with the display screen for the entire scan of aframe.

The present invention is an electroluminescent display system whichovercomes those disadvantages and limitations of the prior art systems.More particularly the electroluminescent display system of the presentinvention includes three electron guns arranged at the vertexes of atriangle, preferably equilateral, the vertexes being at differentelevations. Each gun generates an electron beam which is intensitymodulated by a color signal and which is deflected by suitable forcefields to scan over the area of an electroluminescent display screen forreproducing images thereat. The electroluminescent display screen is athree-color phosphor type display screen with each raster line includingphosphors which emit color radiation corresponding to the primarycolors, i.e., red, green and blue, when excited by an impinging electronbeam. The different color radiating phosphors are arranged at different,fixed elevations within the same raster line.

In the most preferred embodiment of the present invention, the differentcolor radiating phosphors of each raster line are arranged in individualspaced apart horizontally parallel rows, each row including amultiplicity of spaced apart segments of one particular color-radiatingphosphor. The rows of phosphor segments are arranged so that segments ofeach row are aligned vertical ly with those of the other two rows. Thecolor sequence, vertical alignment of the segments and horizontalalignment of the rows are repeated in each raster line. To insure theaccurate reproduction of images, the electron guns are arranged with onegun at the intermediate elevation point equidistant from the other twoguns, and the force fields operated so that each of the rows of phosphorradiating one color are excited by the modulated electron beam generatedby an associated gun.

Because of the arrangement of the different colorradiating phosphor dotsat different elevations, each horizontal row of color radiating phosphorcan be arranged to include a phosphor which radiates only one color whenexcited by an electron beam. Hence, by directing each electron beam toimpinge only the phosphors in one horizontal row during each scan of araster line, the shadow-mask, characteristic of conventional three-gun,three-beam systems can be eliminated. Such a shadowmask-free system iscapable of accurately reproducing exceedingly bright, high resolutionimages. Furthermore, since three electron beams are used simultaneouslyin scanning each raster line, comprised of three separate color rows,the focusing grid wires, large switching power and complex switchingcircuits required by the chromatron systems are eliminated.

Accordingly, it is an object of this invention to provide a simpleelectro-luminescent display system capable of faithfully reproducinghigh resolution images.

More particularly, it is an object of this invention to provide a simpleelectro-luminescent display system characterized by efficiently usingthe scanning electron beams to generate exceedingly bright images.

Another object of this invention is to provide an electroluminescentdisplay system which will not distort the colors of the original scenein producing the image.

A further object of this invention is to provide a dynamic particlefocusing system particularly suited for use in the electro-luminescentdisplay system of the present invention which is capable of convergingthe electrons of each beam to a point which remains coincident with thetarget surface of the display screen for the entire scan of a frame.

The invention possesses other objects and features of advantage, some ofwhich, with the foregoing, will be set forth in the followingdescription of the preferred form of the invention which is illustratedin the drawings accompanying and forming part of the specification. Itis to be understood, however, that variations in the showing made by thesaid drawings and description may be adopted within the scope of theinvention as set forth in the claims.

FIGURE 1 is a diagrammatic cross sectional view of a color televisionpicture tube employing the electroluminescent display system of thepresent invention.

FIGURE 2 is a sectional view of the picture tube of FIGURE 1 taken alonglines 22.

FIGURE 3 is a diagrammatic view of an electron gun assembly.

FIGURE 4 is an enlarged pictorial representation of the phosphor-dotpattern of prior art electroluminescent display screens.

FIGURE 5 is an enlarged pictorial representation of the orientation ofphosphor-dot pattern of the electroluminescent display screen of thepresent invention.

FIGURE 6 is an enlarged pictorial representation of a circular phosphordot pattern embodiment of the display screen of the present invention.

FIGURE 7 is an enlarged pictorial representation of a rectangularphosphor dot pattern embodiment of the display screen of the presentinvention.

FIGURE 8 is an enlarged pictorial representation of a horizontal stripphosphor pattern suitable for use in the electroluminescent displaysystem of the present invention.

FIGURE 9 illustrates the dynamic particle focusing system of the presentinvention, partly in schematic and partly in diagrammatic form.

FIGURE 10 is an enlarged pictorial representation of the rectangularphosphor dot pattern employed in a reversing color sequence embodimentof the present invention.

FIGURE 11 is a block diagram of control circuits employed with thedisplay screen embodiment of FIG- URE 10*.

With reference to FIGURES 1-3, a three-gun color television picture tube11 including the electroluminescent display system of the presentinvention comprises three electron gun assemblies 12, 13 and 14 mountedwithin the neck portion 16 of a conventional picture tube envelope 17.Each gun assembly generates a particular color-related electron beamwhich is guided by suitable force fields to scan the novelelectroluminescent display screen 18 of the present invention. The noveldisplay screen will be described in detail infra.

As portrayed in FIGURE 3, each electron gun assem bly includes anelectron emissive cathode 19 indirectly heated by a filament 21. Thecathode 19 and filament 21 are surrounded by a control grid 22 formodulating the stream of electrons emitted in accordance with aparticular color signal. Initial and final accelerations of themodulated stream of electrons emerging from grid 22 are provided bysuitably charged circular cylindrical electrodes 23 and 24 respectivelydisposed in succession along the path of the electron stream. Thesecond, or final, accelerating electrode 24 is generally charged to avoltage which is an order of magnitude greater than that to which thefirst, or initial, accelerating electrode 23 is charged. The resultantelectric field established therebetween serves to focus the electrons ofthe stream at a point distal the gun assembly. By proper adjustments ofthe static voltages impressed on electrodes 23 and 24, the focal pointof the electrons forming each beam can be made to coincide at thecentric of the display screen 18.

Standard television picture tubes used in reproducing images employ adisplay screen 18 having a target surface 26 which is preferablysubstantially flat. That is with respect to the position of the gunassemblies, the target surface 26 can be considered to have no curvaturesince standard tubes generally have a low curvature relative to thelocation of the gun assemblies. Since each picture element of an imageframe covers a very small area of the target surface 26, generally onthe order of 10 to 10- square inches, and since the axes of the gunassemblies occupy an area of one square inch, the three beams generatedby the gun assemblies 12, 13 and 14 must be converged. T o maintain theconvergence point of the three beams fixed relative to the targetsurface 26 during the entire scan of the flat display screen 18, theangle of convergence of the beams must be changed as they are swepthorizontally and vertically. To carry out standard dynamic convergence,each gun assembly is provided with soft iron pole pieces 27 and 28disposed at each side of the electron stream. The pole piecescommunicate respectively with iron core converging solenoids (not shown)which are energized in the conventional manner by parabolically varyinghorizontal and vertical correcting currents derived by standardtechniques from the vertical and horizontal sweep circuits. In order toconverge all three beams generated, one of the gun assemblies must beprovided with a second set 29 of pole pieces for establishing a magneticfield in quadrature with that established by pole pieces 27 and 28. Thequadrature magnetic field is adjusted so that the three beams convergetoward a single point, so that they will impinge upon three colorphosphors on the target surface.

In accordance with the present invention, the electron gun assemblies12, 13 and 14 are disposed at different elevations within neck portions16 of envelope 17. To facilitate initial convergence of the beams, thegun assemblies are tilted 'a finite amount, generally about 1", towardsthe central axis of the envelope. In one preferred embodiment, the gunassemblies are disposed at the vertexes of an equilateral triangle, thevertexes being at the different elevations. Gun assemblies 13 and 14define the base line of the equilateral triangle, the base line beingoriented perpendicular to the raster lines with gun assembly 12 disposedat an elevation intermediate the elevations of gun assemblies 13 and 14and horizontally displaced therefrom (see FIGURE 2). With the gunassemblies 12, 13 and 14 arranged in the preferred equilateraltriangular array, the possibility of each beam generated by therespective gun assemblies impinging on color radiating phosphorsadjacent to that which is intended to be impinged, hence color overlapand smear, is minimized. Furthermore, by arranging the electron gunassemblies, 12, 13 and 14 at different elevations, and by arranging thedifferent color radiating phosphors of each raster line 33 in separatehorizontal rows 34, 36 and 37 (FIG. 1) in registry with the three beamsissuing from the gun assemblies, each beam generated by each gunassembly can be caused to scan each horizontal raster line 33 withoutinterruption. Hence, in contrast to prior art three-gun systems, theundesirable shadow-mask can be eliminated. As noted hereinbefore theelimination of the shadow-mask enables construction of anelectroluminescent display system which efficiently utilizes itselectron beams to reproduce faithfully highly resolved and brighterimages.

Images are reproduced at display screen 18 by modulating the intensityof the electron beam generated by each of the electron gun assemblies12, 13 and 14 in accordance with a particular primary color signal. Forexample, as shown in Figure 3, the blue color signal is separated fromcomposite television signal by a conventional television receiver 38 andcoupled from output terminal 40 to grid 22 of the blue gun assembly 12.The green and red color signals also are separated from the televisionsignal and coupled from terminals 39 and 41 of receiver 38 to modulatethe electron beams generated by gun assemblies 13 and 14 respectively.For sake of convenience, the gun assemblies 12, 13 and 14 willhereinafter be referred to respectively as blue, green and red guns.

The electron beams generated by the blue. green and red guns aredirected simultaneously by suitable force fields to scan sequentiallythe plurality of raster lines 33 of the picture tube 11. As in standardpractice, each frame is reproduced by interlaced scanning, i.e.,scanning the display screen 18 from left to right and top to bottom,with the image frame being reproduced by scanning the target surface twotimes once along the odd numbered rasters only and once along the evennumbered rasters only. The particular number of raster lines 33 may varyas desired. For example, in the United States and Japan, 525 rasterlines are employed, in most of Europe 625 raster lines, in England 405raster lines and in France 819 raster lines. In any case, the particularnumber of raster lines employed will merely require a particularvertical spacing of the color radiating phosphors comprising the targetsurface 26.

The scanning is accomplished by controlling the force fields inaccordance with the horizontal and vertical sweep signals separated fromthe television signal by receiver 38. Although in the embodimentillustrated in FIGURES l-3. magnetic type beam deflection force fieldsare shown as being used, electrostatic beam deflection force fieldscould be used equally as well. Where magnetic force fields are used todeflect the three beams from the blue, green and red guns, a yoke 42 ismounted about the neck portion 16 of envelope 17 to deflect the beamsemerging from the three color guns. The coils of the yoke 42 areenergized in the conventional manner by suitable vertical and horizontalsweep signals present at the output terminals 43 and 44 of thetelevision reecivers sweep circuits. Referring to FIGURE 2, the mannerin which the magnetic deflection is accomplished is portrayed by poles42 and poles 42", each pair representing respectively the establishmentof the horizontal and vertical field components of the resultantmagnetic beam deflecting field established by yoke 42. The deflectedelectron beams are subsequently accelerated to impinge target surface 26by a post accelerating voltage applied thereto at terminal 45 (seeFIGURE 1).

Considering now the novel display screen of the present invention,attention is directed to FIGURES 4-7. In the figures, horizontal crosshatching represents blue radiating phosphor dots 51; vertical crosshatching, red radiating phosphor dots 52; and inclined cross hatching,green radiating phosphor dots 53. Referring to FIGURE 4, standardphosphor-dot type display screens of conventional color televisionpicture tubes employ triangle three-color phosphor-dot pattern 54arranged to have two different color radiating phosphor dots in ahorizontal line. Furthermore, the phosphor-dot patterns 54 are nested sothat the phosphor-dot patterns 54 of one raster line are separated byportions of the phosphor-dot patterns 54a and 54b of vertically adjacentraster lines. Hence, it is seen that each horizontal row 56 of phosphordots presently include in repeating sequence the three different colorradiating phosphor dots 51, 52 and 53. Consequently, during each scan ofthe raster line, the electron beams must be blanked, for example, by ashadow-mask for approximately twothirds of the scan. As noted hereinbefore, the necessity of blanking has led to many limitations,inconveniences and, in general, a less than desirable reproduction ofthe images. Furthermore, because of the large horizontal spacing ofsuccessive phosphor-dot patterns 54, much color information is lost,thereby degrading the resolution of the image reproduced.

With reference to FIGURE 5, the display screen 18 of the presentinvention employs a unique and superior phosphor-dot pattern 54'. Asshown, the three different color phosphor dots 51, 52 and 53 definingthe patterns 54' are positioned so that their centric points are atdifferent elevations. In the preferred pattern 54', the centric pointsof the phosphor dots 51, 52 and 53 of each pattern 54' are positioned atthe vertexes of an equilateral triangle with two of the phosphor dots,for example, red and green radiating phosphor dots 52 and 53, verticallyaligned. Although, in this configuration there still remains someoverlap of different color radiating phosphor dots in each horizontalrow 56 of phosphor dots, it is seen that the phosphor-dot patterns 54'of each raster line are separated by only two-thirds of the distance ofseparation of the phosphor-dot patterns 54 of the prior art displayscreens as represented by FIGURE 4. Hence, since more picture elementscan be produced during each horizontal scan, the resolution of theimages reproduced by a display screen having a phosphor-dot patternconstructed in accordance with FIGURE 5 will be far superior to thosereproduced by the prior art three-color phosphor-dot display screens asrepresented by FIGURE 4. Furthermore, although blanking would berequired, it is seen that it would be necessary to blank the electronbeams only onehalf the time during each horizontal scan. Hence, brighterimages Will be obtained by using the phosphor-dot pattern of FIGURE 5.It is noted, however, that to maintain vertical resolution, hencesuperior overall resolution, the size of each phosphor-dot should bereduced. It is preferred to reduce their size so that vertical distancecovered by three vertically aligned phosphor dots of the pattern 54' ofthe present invention equals that covered by two vertically alignedphosphor dots of the prior art pattern 54 as represented by FIGURE 4.

In FIGURE 6 another phosphor-dot pattern embodiment employed in thedisplay screen 18 of the present invention is shown which eliminates thenecessity of blanking the electron beams with, for example, ashadow-mask. As illustrated therein, as one possible phosphor dot colorarray, the different color radiating phosphor dots 51, 52 and 53 arearranged in individual rows with the blue color radiating phosphor dots51 substantially interposed between the red and green color radiatingphosphor dots 52 and 53 respectively. The immediately vertically alignedblue, red and green radiating phosphor dots do not form a triangle whichis similar to that formed by the blue, green and red guns 12, 13 and 14.Hence, the position of the blue radiating dots 51 is adjusted so thatthe blue phosphor dots of one generally vertical row of phosphor dotsforms with the red and green dots of laterally adjacent generallyvertical row of phosphor dots the requisite equilaterally triangularthree-color phosphor-dot pattern 54". If the size of the phosphor dotsof pattern 54" is reduced to approximately one-third that of thephosphor-dot pat tern 54 of the prior art as represented by FIGURE 4,the resolution of the image reproduced will be greatly enhanced sinceeach frame reproduced will include considerably more picture elements.

Referring now to FIGURE 7, a most preferred embodiment of thethree-color phosphor-dot pattern used to form the target surface 26 ofthe display screen 18 of the present invention is illustrated. In thisembodiment, the phosphor dots are rectangular and are arranged inhorizontal rows 57 of single color radiating phosphor dots, the phosphordots being vertically aligned. Preferably, the horizontal rows 57 ofdifferent color radiating phosphors are arranged in a verticallyrepeating color sequence, i.e., red, blue, green, red, blue, etc.radiating phosphors. In accordance with the particular arrangement ofthe gun assemblies 12, 13 and 14 of FIGURES 1 and 2, the row of blueradiating phosphor rectangular dots 51 are interposed between an upperrow of red radiating phosphor rectangular dots 52 and a lower row ofgreen radiating phosphor rectangular dots 53'.

Each rectangular dot of the color radiating phosphors are preferablyadjusted to a height-to-width ratio of 1:1.73, for example, 0.014:0.024inch. By constructing the rectangular dots in accordance with thispreferred ratio, the centrics of the red and green radiating phosphordots in one vertical row defines the requisite equilateral triangle withthe centric of the blue radiating phosphor dot of an immediatelylaterally adjacent vertical row.

A display screen 18 having a target surface 26 constructed in accordancewith the phosphor-dot arrangement of FIGURE 7 will be characterized bybeing capable of faithfully reproducing, with high resolution, anextremely bright image. The high resolution is gained as a result of thetarget surface 26 having two times the number of picture elements (eachpicture element defined by a phosphor dot pattern 54) as compared to theprior art display screens constructed in accordance with FIGURE 4.

With the gun assemblies arranged as shown in FIG- URE 2, continuoushorizontal strips 58, 59 and 61 of red, blue and green radiatingphosphors arranged in the color sequence of FIGURE 7 can be employed ina threegun electroluminescent display system. Such a pattern is shown inFIGURE 8. To prevent loss in color fidelity due to interactions betweenadjacently excited points on a phosphor strip, straight conductive wires62 are mounted at regular horizontal intervals, for example, 0.024 inchapart, to extend vertically in front of the phospher strips 58, 59 and61. The wires 62 intercept the electron beams as they are deflected toscan the display screen 18 thereby interrupting the excitation of thecontinuous phosphor strips at regular intervals. The electronsintercepted by the wires 62 are collected by imposing a suitablepositive voltage on the conductive wires 62. While the wires 62interrupt the excitation, there is some migration of excitation throughthe areas which are shielded by the wires. Thus, the resolution obtainedwith this embodiment is not quite as good as that obtained with theconfiguration of FIGURE 7. It is to be noted, however, that theconductive wires 62 do not consume power to the extent that the beamfocusing grid wires of the chromation systems do. This is because theconductive wires 62 are not employed to deflect the electron beams.

To enhance the ability of the display screens of the present inventionto faithfully reproduce images as well as to reproduce images of goodcontrast, it is contemplated that the color radiating phosphor elementswill be separated by finite zones, e.g., 0.005 inch Wide, of lightabsorbing and preferably also non-luminescent, black area 63. (SeeFIGURES 7 and 8.) For example, black manganese oxide or silver particlescould be employed.

In constructing target surface 26 of the three-color radiating phosphordisplay screen 18, any of the known color radiating materials such asthe following can be deposited in the desired pattern on, for example,clear glass; for the red radiating zones, manganese activated zincphosphate; for the green radiating zones, manganese activated silicate;and for the blue-radiating zones, silver activated zinc sulfide. Torender the entire target surface 26 capable of being maintained at auniform potential, the target surface 26 defined by the color radiatingphosphors is covered by a sheet layer 64 of electron permeable highlyreflective conductive material such as silver or aluminum.

Since in the preferred three-color phosphor-dot pattern embodiments ofthe display screen of the present invention, the size of at least onedimension of the radiating phosphors is reduced in comparison to thedimensions of prior art three-color phosphor-dot patterns, it isdesirable to focus the electrons of each beam to a point at the targetsurface 26 for the entire scan of surface 26.

Referring now to FIGURES 3 and 9, in one preferred embodiment of theelectroluminescent display system of the present invention which employsthe substantially flat target surface display screen 18, the focal pointof the electrons forming each of the beams is maintained at the targetsurface 18 by providing each gun assembly with a dynamic cylindricalfocusing electrode 31 interposed be tween segments of electrodes 23 andin register with the electrodes 23 and 24. A suitably varying voltagerelative to electrode 23 is impressed simultaneously on the dynamicfocusing electrodes 31 of the gun assemblies at terminal 32 thereof. Ina manner to be described infra, the varying voltage is selected toautomatically adjust the focus of the electrons forming the respectivestreams so that the focal point of each stream coincides with targetsurface 26 for the entire scan of the display screen. Where the targetsurface 26 has a discernable curvature relative to the location of thegun assemblies, the instantaneous voltage V is varied in directproportion to the variation in the distance between a spherically curvedsurface having its center of curvature at the gun assemblies and thegenerally flat target surface 26 tangent at the centric of such curvedsurface.

If the curvature of surface 26 is considered flat relative to theposition of the electron gun assemblies, the required voltage is definedby the equation:

V is the instantaneous voltage in volts applied to the dynamic focusingelectrode 31 relative to electrode 23;

D is the distance in inches to the furthest point on the target surface26 measured from the centric of surface 26;

d is the instantaneous position in inches of the beam at target surface26 measured from the centric of surface 26; and

V is the voltage in volts required to be impressed on dynamic focusingelectrode 31 relative to electrode 23 to focus the electrons of the beamat point D. Although V will vary depending on the size of the targetsurface 26, the particular potentials applied to electrodes 23, 24, and3 1, the geometry of the electrodes, and the distance between displayscreen 18 and final accelerating electrode 24 as well as other factors,the particular V for any particular color television picture tubeassembly can be empirically determined easily by directing the electronbeam to impinge the target surface 26 at point D and then varying Vuntil the required V is reached that will focus the electrons at thatpoint. Since the centric of target surface 26 is the closest point tothe electron gun assemblies, the voltage applied to electrode 31required to focus the electrons of a beam at other points on the targetsurface 26 will be more negative than that voltage required to focusthem at the centric point.

As can be seen from Equation 1, the voltage impressed at dynamicfocusing electrode 31 varies as a parabolic function of theinstantaneous position of the beam. Hence, the horizontal and verticalconverging currents applied to the converging coils can be used toderive the required varying voltage, V. However, it is to be noted thatseparate suitable function generator or generators could be employed togenerate the requisite varying voltage V. In the former case, a resistor64 is placed in series with the horizontal converging coil associatedwith any one of the beams to derive a voltage which varies as thescanning current through the coil. Similarly, a resistor 66 is placed inseries with the vertical con-verging coil associated with the beam toderive a voltage which varies as the current through the coil. Thevoltages are summed in a voltage summing circuit 67, e.g., a high gainsumming amplifier, which issues a resultant voltage function whichvaries, for example, from zero volts relative to the voltage level atelectrode 23 to some more negative value relative to the voltage levelat electrode 23. The output of summing circuit 67 is applied betweenelectrodes 23 and 31 by leads 68 and 69.

As an illustrative example, for a 25 inch rectangular television picturetube having an aspect ratio of 4:3, having 600 volts direct current(VDC) applied to electrode 23, having 5 kilovolts direct current (KVDC)applied to electrode 24, having parabolically varying currents appliedto the beam converging coils, and the distance from the finalaccelerating electrode 24 to display screen 18 measuring twelve inches,a V equal to 60 volts will focus the electrons of the beams at thetarget surface 26 at the four corners of the rectangular thereof. Thefour corners measure 12.5 inches from the centric of target surface 26.Hence, Equation 1 reduces to Such a varying voltage can be generated bycombining a voltage issuing from summer 67 and derived from theparabolically varying current applied to the horizontal convergence coilwhich varies from 38 v. to 0 v. to 38 v. with a voltage issuing fromsummer 67 and derived from the parabolically varying current applied tothe vertical convergence coil which varies from 22 v. to 0 v. to 22 v.Since these varying voltages are derived from the horizontal andvertical sweep circuits, their addition in the proper manner will beautomatically synchronized with the sweep of the beams over the targetsurface 26 of display screen 18. It is to be noted that dynamic focusingelectrodes 31 of each gun assembly 12, 13 and 14 can be controlled bythe same voltage function V.

Referring to FIGS. and 11, another embodiment of the electroluminescentdisplay system employs an electroluminescent display screen includinghorizontal rows of red, blue and green color radiating phosphor dots 71,72 and 73 respectively, arranged vertically in a reversing colorsequence, i.e., a red row 71, a blue row 72, a green row 73, a blue row72, a red row 71, a blue row 72", a green row 73, etc. In the embodimentillustrated in FIG. 10, the rows of red and green radiating phosphorsare employed in two vertically adjacent rasters, for example, green row73 is used in both vertically adjacent rasters 76 and 74. Hence, whenthe electron beams are deflected to scan vertically adjacent rasters,the red color information must be delivered to the normally consideredred gun 14 during the scan of one raster and the normally consideredgreen gun 13 during the scan of the vertically adjacent raster.Similarly, the green color information must be delivered to thedifferent guns 13 and 14 during the scan of vertically adjacent rasters.

Referring to FIG. 10, it is noted that the vertical color sequence ofthe horizontal rows of color radiating phosphors is the same inalternate raster lines. Hence, since in interlaced scanning, alternateraster lines are scanned during a particular scanning of the targetsurface, it is necessary to switch the delivery of the red and greencolor signals only after each complete scan of each raster of the targetsurface. One electronic circuit for accomplishing the above notedswitching of the delivery of the color signals is shown in FIG. 11. Theswitching means is electrically coupled between terminals 39 and 41 oftelevision receiver 38 (see FIG. 3) and the electron guns 13 and 14. Theswitching is accomplished by coupling first and second electronic gates78 and 79 to receive the red color signal information from terminal 39of television receiver 38 via input terminal 39'. Third and fourthelectronic gates 81 and 82 are coupled to receive the green color signalinformation from terminal 41 via 41'. Gates 78 and 79 are maintained inopposite conducting states with the output of gate 78 connected viaterminal 83 to the control grid 22 of red gun 14 and the output of gate79 connected via terminal 84 to the control grid 22 of the green gun 13.Similarly, gates 81 and 82 are maintained in opposite conducting states,with gate 82 in the same conducting state as gate 7 8. The outputs ofthe gates 81 and 82 are connected respectively to terminals 83 and 84.

To control the conducting states of the gates, the output of the firsthalf of a triggered bistable multivibrator 86 is coupled via terminal 87to the control electrode of gates 78 and 82, for example the controlgrid of a pentode tube coincidence amplifier. The output of the secondhalf of bistable multivibrator 86 is coupled via terminal 88 to, forexample, the control grid of coincidence amplifier gates 79 and 81.Where vacuum tubes are employed in constructing the bistablemultivibrator 86, a negative pulse is derived from the vertical retracesignal generated in the vertical synchronizing circuit of the televisionreceiver 38 and coupled simultaneously via terminal 89 to the platecircuits of the multivibrator 86. As in conventional practice, each timea negative pulse appears at the plates of the tubes comprising themultivibrator 86, the conduction state of each tube changes. Hence, thevoltage level at the output terminals 87 and 88 will change as will theconduction state of the gates. In this manner the color signalinformation will be delivered to the proper electron gun assembly duringthe reproduction of images at the target surface.

While the invention has been described with respect to several specificembodiments thereof, may variations are possible. For example, it shouldbe realized that the vertical sequence of each three rows of the primarycolor phosphors is unimportant and that any other sequence other thanthe red, blue and green sequence shown in the figures may be used. Theinvention is only to be considered limited by the claims.

What is claimed is:

1. An electroluminescent display system for reproducing color imagescomprising three electron guns for generating three electron beams, eachof said electron guns positioned at a different elevation, a displayscreen disposed to receive said electron beams on a surface thereofcomprising three different color radiating materials responsive toelectron impingement, each of said different color radiating materialsdisposed on said surface in separate horizontal rows in a repeatingcolor sequence with adjacent rows of material radiating a differentcolor upon electron bombardment, means for generating a force field fordeflecting simultaneously said electron beams horizontally across saidsurface sequentially at selected different successive verticalelevations, said horizontal rows of color radiating material arranged sothat said electron beams coincide individually with three adjacenthorizontal rows of color radiating material during each horizontaldeflection across said surface, said electron guns being positioned atthe vertexes of an equilateral triangle with two of said guns verticallyaligned, each horizontal row being defined by a plurality of segments ofcolor radiating material, said segments arranged so that the segments ofthree adjacent horizontal rows define an equilateral triangle, saidsegments being rectangular, and vertically aligned, each segment havinga height-to-width ratio of 1:1.73, said display screen beingsubstantially flat, and said rectangular segments being separated fromtheir adjacent rectangular segments by zones of light absorbingmaterial.

2. An electroluminescent display system for reproducing color imagescomprising three electron guns for generating three electron beams, eachof said electron guns positioned at a different elevation, a displayscreen disposed to receive said electron beams on a surface thereofcomprising three diiferent color radiating materials responsive toelectron impingement, each of said different color radiating materialsdisposed on said surface in separate horizontal rows in a repeatingcolor sequence with adjacent rows of material radiating a differentcolor upon electron bombardment, means for generating a force field fordeflecting simultaneously said electron beams horizontally across saidsurface sequentially at selected different successive verticalelevations, said horizontal rows of color radiating material arranged sothat said electron beams coincide individually with three adjacenthorizontal rows of color radiating material during each horizontaldeflection across said surface, said electron guns being positioned atthe vertexes of an equilateral triangle with two of said guns verticallyaligned, said horizontal rows of different color radiating materialbeing arranged in a reversing repeating color sequence, and switchingmeans electrically connected to said vertically aligned electron gunsfor alternately coupling a first color signal information to the lowerand uppermost electron gun and a second color signal information to theupper and lowermost electron gun in synchronism with the each scan ofthe entire target surface.

3. An electroluminescent display screen for use in a color televisionpicture tube comprising a light pervious sheet defining a regularsurface, a plurality of horizontal rows of segments of electronresponsive red radiating material, a plurality of horizontal rows ofsegments of electron responsive blue radiating material and a pluralityof horizontal rows of segments of electron responsive green radiatingmaterial, said horizontal rows of red, blue and green radiating materialdisposed vertically on said surface in a repeated color sequence, saidsegments of material being rectangular and said color sequence beingdefined by three adjacent horizontal rows, said segments in saidhorizontal rows being vertically aligned, each segment having aheight-to-width ratio of 1:1.73, and said regular surface beingsubstantially flat.

4. The apparatus according to claim 3 further comprising a layer ofelectron permeable highly reflective conductive material disposed tocover said horizontal rows of material, and wherein said rectangularsegments are separated from their adjacent rectangular segments by zonesof light absorbing material.

5. In an electron gun assembly including an initial acceleratingelectrode maintained at a given first voltage and an adjacent finalaccelerating electrode maintained at a given second voltage higher thansaid first voltage for accelerating and directing electrons of a beam toimpinge a target surface of a given size and being positioned at a givendistance from said gun assembly and said beam being scanned over saidtarget surface by a force field, the combination therewith comprising; adynamic focusing electrode insulatingly interposed between segments ofsaid initial accelerating electrode; a varying voltage generatorproviding a voltage output which varies, during the scanning of thebeam, substantially according to the variation in distance between saidgun assembly and said target surface; and means for coupling saidvarying voltage from said generator to impress same on said dynamicfocusing electrode relative to said initial accelerating electrode tofocus said electrons of said beam at the target surface.

6. The apparatus according to claim 5 wherein said varying voltagegenerator provides a voltage output which varies substantially accordingto the equation where V is the instantaneous voltage in volts providedby said generator, D is the distance in inches to the furthest point onthe target surface measured from the centric of said target surface, dis the instantaneous position in inches of the beam at said targetsurface measured relative to its centric point during the scanning ofsaid beam, and V is the voltage in volts required to be impressed onsaid dynamic focusing electrode relative to said initial acceleratingelectrode to focus said electrons of said beam at point D.

7. A color television system comprising a picture tube employing threeelectron gun assemblies positioned at different vertical elevations andeach of which includes an initial accelerating electrode maintained at agiven first voltage and an adjacent final accelerating electrodemaintained at a given second voltage higher than said first voltage foraccelerating and directing electrons of a beam to impinge a targetsurface of a given size positioned at a given distance from said gunassemblies; means for pro viding a force field for scanning-together thebeams from said guns over said target surface; said means deflectingsaid beams over said target surface in sequence at selected differentsuccessive vertical elevations; a dynamic focusing electrodeinsulatingly interposed between segments of said accelerating electrodeof each of said gun assemblies; a varying voltage generator providing avoltage output which varies, during the scanning of the beam,substantially according to the variation in distance between said gunassembly and said target surface; means for coupling said varyingvoltage from said generator to impress same on the dynamic focusingelectrode relative to their respective associated initial acceleratingelectrodes to focus electrons of said beam at the target surface; saidtarget surface comprising three different color radiating materialsresponsive to electron impingement, each of said different colorradiating materials disposed on said surface in separate horizontal rowsin a repeating color sequence with adjacent rows of material radiating adifferent color upon electron bombardment, said horizontal rows of colorradiating material arranged so that said electron beams coincideindividually with three adjacent horizontal rows of color radiatingmaterial during each horizontal deflection across said surface.

References Cited UNITED STATES PATENTS 2,792,521 5/1957 Sziklai et a1.3l5l3 X 3,018,405 1/1962 Oxenham 31392 X 3,028,521 4/1962 Szegho 31513RICHARD A. FARLEY, Primary Examiner.

M. F. HUBLER, Assistant Examiner.

